In a variety of technical working procedures when processing materials, for example, when machining materials, it is advantageous to provide lubrication and/or cooling at the processing point to increase process reliability in order, among other things, to ensure the perfect functioning of a tool and to increase its service life.
In order, for example, to keep down the costs for the respective lubricant and/or coolant and the amount spent on cleaning the environment and the products produced and, in addition, to keep down the impact on the environment and on the health of the operating personnel, attempts have already been made to manage with small flows of lubricant and/or coolant. This approach is already known by the term “minimum quantity lubrication” (MQL), a corresponding system is usually designated as a “minimum quantity lubrication system” (MQL system). Usual lubricant flows and/or coolant flows in such minimum quantity lubrication systems comprise flow rates of, for instance, around a maximum of 50 ml/h and typically approximately between 10 and 50 ml/h, the lubricant or coolant being supplied to the tool/workpiece in the usual manner as an aerosol.
An aerosol is to be understood, in general, as a heterogeneous mixture or a dispersion produced from solid or liquid airborne particles in a gas. The airborne particles contained in the aerosol are also called aerosol particles or aerosol particulates or aerosol droplets. The behavior of an aerosol depends in the majority of cases on the particles and on the carrier gas. An aerosol as a whole or unit substantially comprises a dynamic, flowing, fluid-like behavior or fluid-like characteristics. In the case of such lubrication systems, for example, for machine tools or motor spindles or the like, a lubricant and/or coolant or a so-called “cooling lubricant” is usually used for the aerosol particles, additives for corrosion protection, emulgation, stabilization, de-foaming, etc. being contained, in particular, along with water and oils.
To date, the difference has been made in the majority of cases in practice between so-called two-duct minimum quantity lubrication systems (from now on designated in short as so-called two-duct MQL systems), as are disclosed, for example, in DE 196 55 334 B4, and so-called single-duct minimum quantity lubrication systems (from now on designated in short as so-called single-duct MQL systems).
In the case of so-called two-duct MQL systems, the aerosol is not generated until close to the tool holder, frequently by means of separately supplied lubricant and/or coolant as well as compressed air, in order to avoid relatively long aerosol transport paths and to enable as rapid as possible reaction times in the case of adaptations/changes to the required quantities of lubricant and/or coolant. Correspondingly, lubricant and/or coolant and air are run through the tool spindle in two separate ducts and the aerosol is only formed at the or in the vicinity of the rotatable/rotating tool holder.
In the case of so-called single-duct MQL systems, an aerosol generator, which is separate to the spindle or motor spindle or is arranged externally/outside and in which the aerosol is generated from lubricant and/or coolant and compressed air, is usually provided in practice. The aerosol is injected/fed, for example, into an aerosol line or aerosol transport line and from there is supplied, among other things, via rotary feedthrough, spindle/motor spindle and tool holder to the tool/workpiece.
In general, the transport of the aerosol is effected by means of flowing air or compressed air and is usually controlled, in this connection, by the pressure of the (compressed) air. In particular, the direction of transport or the direction of flow is through the path that the compressed air takes, and the velocity of flow/speed of flow of the aerosol is also at least determined by the pressure of the compressed air.
It has been shown in the meantime in practice that in the case of so-called single-duct MQL systems, in particular, when used with machines with spindles, the transport of the aerosol through the spindle can cause problems which result in the aerosol feed or the quantities of lubricant and/or coolant flowing to/arriving at the tool/workpiece being smaller than actually provided/required. Thus, among other things, losses occur as a result of the aerosol particles condensing sometimes to a large extent, among other things, on the transport lines and/or being lost inside the spindle as a result of leakages, which results in a disadvantageous increase in the quantities of lubricant and/or coolant to be used and in unwanted contaminants in the spindle such that the desired effects of the minimum quantity lubrication are no longer realized in a sufficient manner.